java-gclog-graph is a script to generate graph from Java garbage collector log.

Features

• Generate PNG image from Java garbage collection log
• Parallel garbage collector - default for Java 1.8 - is supported
• G1 garbage collector - default for Java 11, Java 17, Java 21 - is supported

Installation

Standard Environment

• Copy the java-gclog-graph.py or clone the repository to destination directory
• Install required packages - usually it is only matplotlib package to install

Python Virtual Environment

git clone https://github.com/pes-soft/java-gclog-graph
virtualenv java-gclog-graph/venv
java-gclog-graph/venv/bin/pip install matplotlib

Usage

./java-gclog-graph.py --help

This will show the help and supported switches:

usage: java-gclog-graph.py [-h] [-f LOGFILE] [-o OUTPUT] [-d DATETIME_FORMAT] [-t TAIL_TIME] [-m {change,after,before}] [-V]

• -f, --logfile LOGFILE : Path to the input GC log file
• -o, --output OUTPUT : Path to the output PNG file (default is ./java-gclog-graph.png)
• -d, --datetime-format DATETIME_FORMAT : Format of timestamp in GC log (default is ISO 8601: %Y-%m-%dT%H:%M:%S.%f%z)
• -t, --tail-time TAIL_TIME : Graph only the last seconds before the last data entry (supports suffix m,h,d,w; default is to graph all)
• -m, --heap-mode {change,after,before} : Graph heap change either before GC, or after GC, or as a line with heap change (default is line with change)
• -V, --version : Print current version and exit

Examples

Parse log in /app/javaapp/logs/gc-2025-06-08_17-07-28.log, save output to /app/javaapp/reports/gclog-CURRENT_DAY.png, graph only entries from the 2 last days since the last event in the log:

./java-gclog-graph.py -f /app/javaapp/logs/gc-2025-06-08_17-07-28.log -o /app/javaapp/reports/gclog-$(date +%a).png -t 2d

Parse logs that have been modified earlier than 2 days ago in directory /app/javaapp/logs matching with file name regexp gc-*.log, sorted by date of last modification and graph only entries from the 1 last day since the last event in the log:

./java-gclog-graph.py -f <(find /app/javaapp/logs -mtime -2 -name 'gc-*.log' | xargs -d "\n" ls -tr | xargs -d "\n" cat) -o /app/javaapp/reports/gclog-$(date +%a).png -t 1d

Graph Samples

Java 1.8 Parallel garbage collector log processed, with limit on the recent 1 day, in default "change" heap mode.